Erederik alfred johnsen and knud rahbek



Feb. 27, 1923. 1,446,748.

l F. A.'JOHNSEN ET AL'. y

ELEcTAoscoPlc APPARATUS.

Patented Feb. 27, 1923.

UNITED srArs FREDERIK ALFRED JOHNSEN AND KNUD RAHBEK, COPENHAGEN, DENMARK.

l ELEcTRoscorIc APPARATUS;

Application led July 16,

- To all whom t may concern:

Be it known that we, FREDERIK ALFRED JoHNsEN and KNUD RAIIBEK, subjects of the Kin of Denmark, residing at Copenhagen, len'mark, have invented new and useful Improvements in Electroscopic Ap.-

paratus, of which the following is a speci ication.

The invention relates to electrostatic apparatus of the kind in which the attraction between two members, having an electrical potential diference, producesv a relative movement of said members, thereby indicating the existence of the said difference of potential. A If instead of air another dielectric, for

, instance a solid dielectric, is located between the two members, the attraction will increase at a degree corresponding to the rela'- tion between the dielectric-constants of the air and of the dielectric concerned. This fact, however, is utilized in prior apparatus of this kind in part only, as between the two bodies a recognlzable air space along lthe entire length of the members is present, besides the dielectric. l

The attractive force, therefore, will only be relatively small, and for this reason the prior apparatus are usable only in the event of relatively high voltage. The said' air space is therefore detrimental for the eii'ect.l

This drawback isavoided according to the present invention, in that the conductive elements and the body of low conductivity are arranged relatively to each other in such manner that the low conductive member is tangent to one or both of the conductive members and diverges by slow degrees from the said member or members.

Owing to the divergence betweeny the conductive and the low-conductive members the air-space immediately close to the place .of contact between the members will be ininitely small and at the said place the attraction between the said members will therefore have a relatively high value. At least one ofthe said members is formed as a thin, flexible strip, which'when attracted, is.adapted to fold'itself upon the surface of one of the other members. tion quite close-to the place of contact surpasses the elastic stress of the said strip, the conductive and low conductive .members will be folded upon one another in the neighborhood of the placeof contact; thereupon the place of contact and the line of the said atrelay.

If the attrac- 1919. Serial N0. 311,385.

tract-ion will move a little along thesurfacel `Figs. 2. to 5, diagrammatically, four various manners of construct-ing the condenser,

Fig. 6 a longitudinal section of 'an electroscopic apparatus,

Fig. 7 a. longitudinal section of a modified construction of the same,

Fig. 8 a longitudinal section of an electroscopic apparatus designed for pocketwear, and

Fig. 9 a troscopic apparatus constructed as a static In Fig.v 1, 1 is the dielectric, which is in irm connection and in eiiicient contact with the slightly curved surface of the one condenser plate Q. The other plate is formed by ay resilient and slightly flexible conductive strip 3 whose lower end, in the igure, is constantly held pressed against the substance 1, or is cemented tothe same, so that the strip 3 and the substance 1 are just touching each other tangentially, about at the section 5. If the strip is supported by a separate holder 6, the strip has only to touch the substance 1 lightlyr at the section 5, and even a. small air-space at this point will ordinarily do no harm, provided that it does not exceed a fraction of a millilongitudinalsection of an elecmeter, and the length of the strip 3 between the holder 6 and the section.5 is not too small. In both cases, a potential difference between the met-al 2 and the strip 3 will have the effect that the strip, in the .very neighborhood of the section 5,' where the airgap is zero or infinitely small, is pulled quite forcibly towards the substance 1, the attraction overcoming the elastic lresistance to bending of the strip, and thereby causing points of the strip 3 immediately above the section 5 to touch the-substance 1. At the p resulting new points of contact between the substance 1 and the strip 3, there will then be acting an equally large attractive force, and the result will be that thev entire strip 3 from. the section 5 and upward, will cling tightly yto the .substance 1 as indicated by the position 4 shown by dotted lines in Fig. 1. Thus the strip 3 especially at its upper end performs a very appreciable movement. The relatively large electric forces acting` progressively, during the bending, upon the successive points of the strip render it practicable t0 use so stiffI a strip 3 that an electroscopic apparatus constructed according to this principle may be used in all positions, and will stand transportation.

An especially great sensitiveness is attained by using as the dielectric a suitable semi-conductor, i. e., a materiall which has a certain slight conductivity without how-v ever being a conductor. Such materials a-re stated in our British patent specification No. 144,761.

` If the dielectric is thin, it may be firmly connected to Ithe strip 3 as shown in Fig.

2, so that the said strip and the dielectric together form a flexible strip, which may apply itself closely against the plate 2. This plate may also be coated with a dielectric film 7 (Fig. 3). As shown in Fig. v4, the dielectric 1 may also be a separate piece 8, while both the plates 2 and 3 are curved and flexible and adapted to perform the movement towards the substance 8 simultaneously.

Finally, there may be used two flexible curved films 9 (Fig. 5) touching one another tangentially, their outerv faces being fitted with conductive coatings forming` the plates 2 and 3.

In Figs. 6 and 7, the arrangement in Fig. 1 1s` shown enclwmE in a casing 7, for instance a tube or the like with outer terminals 10 and 11. This' entire arrangement forms thus an electroscopic apparatus. Unle the enclosing case 7 be transparent, it may be fitted with -a window or opening 12, through which the motion of the strip 3 may be observed.

Between the `plate 2 and the terminal 10, there may be inserted a large ohmic resistance 13. If the. dielectric 1 (Fig. 1) has only a very slight conductivity, the resistance 13 may amount to several megohms,

without injuriously affecting the sensitiveness of the apparatus. which may consist of some semi-conducting material or some insulating body powdered with graphite or the like, protects the cir- .cuit wherein theelectroscopic apparatus is inserted against ybeing shortcircuited in consequence of' any insulation fault or a puncture of the dielectric 1. A large ohmic resistance like thiemay also be inserted bel tween the termiml'll andthe strip 3.

An electroscopic apparatus of this nature may be used for ascertaining whether a wire from a generating station. is grounded or not, one of the terminals being simply This resistance 13 atraves held in the hand, while the other terminal is brought into contact with the wire concerned. l

In this case, the resistance 13' acts as protection against dangerto the person using the apparatus. v

Fig. 8 shows, in natural size, an apparatus ofl this kind', designed for the pocket. Here the plate 2 is a slightly curved metal sheet coated With the dielectricl 1 and held in position by a metal post 14wlhich is fastened in the insulating tube 15 (of ebonite or the like). At the end of the tube 15, ,there is provided a metal point 17 conductively connected, by way of a graphite resistance 16 (or a similar highresistance), with the members v14 Iandl 2. The flexible strip 3 is connected, by a clip 18 fitted with a contact-spring, with a metal casing 19 which is fitted, at the top, with an opening 20 covered with glass or the like and allowing inspection of the motion of an indicator 23 and 24 which are touched by the strip in its two extreme positions. 1f the terminal." 10 and 11 are exposed to a tensionE, the strip 3 will break the circuit G and close the circuit F. An apparatus of this kind may be utilizedffor all known uses of static relays, it may for instance release an alarm device, or it may cause earthing of a conductor (fo-r instance a low-current wire) which for some reason, for instance by coming into contact with a heavy-current wire, has received an abnormally high potential above, earth, etc. A

Whatwe claim is :f-

l 1. An electroscopic apparatus'comprising diverging conductive members, at least one at least one of said three members being` fixed near one end, where the low-conductive member and one of the conductive members touch one another, diverging therefrom at a gradually increasing rate.

- 2. fAn el'ectroscopic apparatus comprising diverging .conductive members, one of which is exible, and a low-conductive member between said yconductive members, one of said three membersbeing fixed near one end, where the low-conductive member and one of the conductive members touch one another, diverging therefrom at a gradually increasing rateLthe elasticity of the members enabling them to be folded one upon another by mutual electrostatic attraction due to a potential dierence applied to said members.

3. An electrosqopic 1{apparatus nom rising diverging conductive members, at east one of which is iexible, and a low-conductive member between said conductive members, one of said three members being. fixed near one end, where the low-conductive member touches one of the conductive members, diverging therefrom at a gradually increasing rate, the low-conductive member forming a cover on the surface of one of the conductive members, the elasticity of the members en. abling them to be folded upon one' another by mutual electrostatic attraction .due to a potential difference applied to the said members.

4. An electroscopic apparatus comprising diverging conductive members, at least one of which is iexible, and a low-conductive `member between said conductive members,

touches one of the conductive members, diverging therefrom at a aduall increasing degree, the low-oonductlve mem r forming l a cover on the surface of one of the conductive members' and the surface on vthe other conductive member facing the low-conductive member being covered with a layer of signed our names in the presence of two subscribing Witnesses.

FREDERIK ALFRED JoH-NsEN. KNUD RAHBEK.

Witnesses:

CARL HEMMINGREN, JULIUs LEHMANN. 

